1. Field of the Invention
The present invention relates to a transmission line in which signal conductors that transmit high-frequency signals of different frequencies are located close to each other.
2. Description of the Related Art
In the related art, various kinds of transmission lines that transmit high-frequency signals have been developed. For example, a transmission line described in Japanese Patent No. 4962660 has a stripline structure. The transmission line described in Japanese Patent No. 4962660 includes a dielectric base body having an elongated shape, a signal conductor, a first ground conductor, and a second ground conductor. The signal conductor is disposed at a midway position in a thickness direction of the dielectric base body. The signal conductor is included between the first ground conductor and the second ground conductor in the thickness direction of the dielectric base body. The first ground conductor and the second ground conductor are connected to each other by a plurality of via-hole conductors arranged along the signal conductor. The above configuration provides a transmission line having a stripline structure in which the signal conductor is located between the first ground conductor and the second ground conductor.
When a plurality of transmission lines having the configuration described in Japanese Patent No. 4962660 are located close to each other in a device such as a communication device, for example, a plurality of signal conductors are typically arranged in one dielectric base body. Accordingly, the plurality of signal conductors may be spaced apart in a direction perpendicular to the thickness direction of the dielectric base body.
That is, the transmission lines, each including the structure described in Japanese Patent No. 4962660, may be arranged in the direction perpendicular to the thickness direction of the dielectric base body.
As electronic devices to which the transmission line is mounted become smaller, it is desirable to reduce the size of the transmission line. However, if neighboring signal conductors are located close to each other, coupling occurs between the signal conductors. For example, according to the above-described configuration, a distance between the signal conductors decreases if the width of the transmission line is narrowed, which increases coupling between the signal conductors. As a result, isolation between transmission lines including the signal conductors decreases.